WINE, CHEMISTRY AND MANUFACTURE OF. Before entering into the chemistry of this subject, it is necessary that the composition of the grape, from whose juice it is de rived, should be understood; and as there is an immense variety of vines yielding grapes of corresponding variety, and as the saute variety* will, under different external influ ences, produce very different grapes, it is obvious that our-researches must be confined to the most typical form of grapes. The principal component of the juice of ripe grapes is water, in which are various substances, either held iu solution or very minutely di vided. The juice as obtained by pressure, is thick, and exposure to the heat of the sun rapidly changes it into a fermented liquid. As principal components lick( in solution in the water, professor Mulder mentions "sugar (both grape-sugar and fruit-sugar), gela tine or pectiue ; gum, fat, wax, vegetable albumen, vegetable gluten, and sonic other substances of the nature of extractive matters, which are not, however, accurately de termined; tartaric acid, both free and combined with potash (as cream of tartar), partly also combined with lime • in some cases, we find also racemic acid, malic acid, partly quite free, partly combined with lime, and, according to some, tartrate of potash and alumina; further, oxide of manganese and oxide of iron, sulphate of potash, common salt, phosphate of lime, magnesia, and siPcic acid may also exist."—Chemistry of Wine, p. 5. Although no other ingredients have as yet been discovered in grape-juice, others, which only appear during fermentation, and impart not only the vinous smell common to all wines, but the aroma (bouquet) and the flavor peculiar to each wine, must exist in it in small quantities. In those cases where the skins are allowed, as in the preparation of red wine, to ferment with the juice, the constituents imparting odor and flavor may be drawn from them. Coloring matter and tannic acid are undoubtedly found in the skin, and are thus imparted to red wines. Moreover, the grape-stones, which are left with the skins, yield tannic acid freely fermentation. The different proportions in which the inorganic matters—the potash, soda, lime, magnesia, iron, manganese, sulphuric acid, phosphoric acid, and chlorine—exist in grape-juice, exert a very great influence upon the quality of the wine, both in relation to its color and its taste. A relative excess of
phosphoric acid, or of lime, or of soda, will induce changes sufficiently obvious to the chemist, but which we have not space to discuss. With regard to the acids of grape juice, or must, as it is technically called, professor Mulder observes that, as a general rule, the three—viz.., tartaric, maim, and citric—are rarely found together in one fruit, and he doubts whether the presence of citric acid has been fully proved. Malic acid exists in unripe, and tartaric acid in ripe grapes; and while no malic acid exists in wine made from perfectly ripe grapes, a small quantityls present in most wines. In the tide TARTARIC ACID, it is shown that a nearly allied acid racemic acid, exists in excep tional cases in grapes. The quality of wine is only affected if this acid be largely present, because less lime than usual will be found in it, racemate of lime being less soluble than tartrate of lime, and further, because cream of tartar is more soluble than hiracemate of potash. Such wines are consequently sweeter, and—if red wines—darker colored, than wines containing only tartaric acid. The quantity of sugar varies extremely. In the juice of very ripe grapes, it may reach 40 per cent. According to Fontenelle, the juice produced in the s. of France contains from 30 to 18 per cent, while in the neigh borhood of Stuttgart, Reuss determines it at from 25 to 13 per cent. In ilic low and variable temperature of Holland, the juice of the best grapes yields only 10 or 12 per cent of sugar. The composition of the albuminous matter is not clearly determined. In an analysis of the must of the Riessling grapes of Grumbach, Heitz found that the gluten (no albumen was found) was thirty times less abundant than the sugar. It prob ably varies at from 1 to 4 per et-nt. The only other ingredient requiring notice is fat, which is chiefly but not entirely derived from the grape-stones, in which it is an abund ant ingredient. It occurs in wine, in minute quantity, in the form of a fatty acid.